1. Field of the Invention
The invention concerns a device and a method for automatically adapting a light sensor to the light transmission characteristics of a windshield of a vehicle, wherein the light sensor is allocated to an automatic control device for switching lighting devices of a motor vehicle on and off and wherein the light sensor is located in an area of the windshield.
2. Background Art
A control device of the type in question is known from DE 195 23 262 A1. The control device is associated with a light sensor having an ambient light sensor for the nondirectional determination of general light conditions (brightness) in the vehicle surroundings and an oriented directional sensor for determining the light conditions in the driving direction. The light sensor is connected to an electronic evaluation device. The evaluation device takes into account the signals of both the sensors and the current switching state of the lighting devices to determine whether a change in the switching states of the lighting devices is required. As a result of this known control device, the automatic switching on and off of the lighting device of a vehicle is in principle possible in many situations with changing light conditions, such as the onset of night or long drives through tunnels.
The light sensor associated with the control device is located behind the windshield, approximately in the area of the base of the rearview mirror. On one hand, this location allows the determination of ambient brightness which is affected only slightly by the vehicle, and, on the other hand, it is nearly ideal for measuring the direction specific brightness in the driving direction. A drawback of this location is that the light flux received by the individual sensors must first pass through the windshield where, under certain circumstances, its properties change. This is particularly true in the case of current vehicle designs, where heat-insulated glass is increasingly used, which, as a result of the absorption or reflection of infrared radiation into the visible spectrum, changes the spectral composition of the light, or, in the case of so-called color prisms used in the upper area of the windshield, which have a strong filtering effect on the visible spectrum.
Accordingly, it is an object of the present invention to provide a device and a method for automatically adapting such a control device, particularly the light sensor assigned to it, to the light transmission properties of each given windshield.
In carrying out the object and other objects, the present invention provides a device and a method in which the transmission properties of the windshield are determined at at least two different wavelengths and compared with known reference values.
Further, in carrying out the object and other objects, the present invention provides a device for automatically adapting a light sensor to light transmission characteristics of a windshield of a vehicle. The light sensor is associated with an automatic control device for switching lighting devices of the vehicle on and off and is located adjacent the interior side of the windshield. The device includes at least one light receiver located adjacent the interior side of the windshield for receiving a light beam. A light transmitter is located adjacent the interior side of the windshield for transmitting a light beam having at least two different fixed wavelengths in the visible and/or infrared light spectral range. A light conducting body couples the light beam transmitted from the light transmitter to the at least one light receiver along a path which includes transmission through the windshield and at least one reflection on the exterior side of the windshield.
The device may further include a memory unit for storing light intensity reference values associated with each fixed wavelength of the light beam. A processor may compare light intensity values of each fixed wavelength of the light beam received by the at least one light receiver with the light intensity reference values in order to adapt the light sensor to the light transmission characteristics of the windshield. The light transmitter may include a light emitting diode operable for transmitting a visible light beam at three different fixed wavelengths.
Also, in carrying out the object and other objects the present invention provides a method for automatically adapting a light sensor to light transmission properties of a windshield of a vehicle. The light sensor is associated with an automatic control device for switching lighting devices of the vehicle on and off and is located adjacent the interior side of the windshield. The method includes transmitting a light beam having at least two different fixed wavelengths xcexl, . . . , xcexn from at least one light transmitter located adjacent the interior side of the windshield. A light conducting body couples the light beam transmitted from the light transmitter to at least one light receiver located adjacent the interior side of the windshield along a path which includes transmission through the windshield.
The light intensities Il, . . . , In. Of each of the at least two different fixed wavelengths xcexl, . . . , xcexn of the light beam received by the at least one light receiver are then measured. The measured light intensities Il, . . . , In are compared with reference light intensity values Ir1, . . . , Irn Transmission properties of the windshield are then calculated based on the comparison between the measured light intensities I1, . . . , In and the reference light intensity values I1, . . . , In. Operating parameters of the automatic control device or of the light sensor are then influenced as a function of the calculated transmission properties of the windshield.
The step of calculating may include determining the type of the windshield from the calculated transmission properties of the windshield. The step of influencing may include influencing operating parameters of the control device or of the light sensor as a function of the determined windshield type.
The reference light intensity values Ir1, . . . , Irn are the reference light intensity values of a pane of clear glass for each of the at least two different fixed wavelengths xcex1, . . . , xcexn of a light beam received by a light receiver from a light transmitter along the path.